The present invention provides a foreign matter detecting method capable of realizing high precision of foreign matter detection or simplification of device adjustment, being equivalent to an opticaldetecting mechanism. A plate-like detection plate portion that undergoes strain due to contact with an object is used for detecting the presence of an object that can come into contact with a liquid ejecting unit with relative movement between a medium and the liquid ejecting unit, and is provided with a piezoelectric film sensor that outputs an electric signal corresponding to strain of the detection plate portion. The piezoelectric film sensor includes a detection film portion in which a piezoelectric element that causes a voltage change corresponding to the strain is arranged, and an outputcircuit portion that converts the voltage change of the detection film portion into an electric signal and outputs the electric signal. The output circuit portion is provided on a second plate surface, which is a rear surface of a first plate surface facing the medium, of the detection plate portion.